1. Field of the Invention
This invention relates to a pump device and an ink jet recording apparatus having the pump device, and more particularly to a pump device suitable for use as recovery means used for the recovery of the normal operation of an apparatus dealing with liquid, such as an ink jet recording apparatus, and to an ink jet recording apparatus having such pump device.
2. Related Background Art
For example, an ink jet recording apparatus has heretofore suffered from clogging of the nozzle thereof by dust or solidification of liquidous ink or unsatisfactory discharge of ink caused by bubbles entering into the nozzle.
As the means for preventing the unsatisfactory discharge as described above, there are generally known a method of pressurizing ink by a pump and forcing dust or the like out of the fore end of the nozzle and a method of reducing the pressure of the ink and sucking out dust or the like from the fore end of the nozzle.
Of these methods, pressurizing the ink is more advantageous in obtaining great pressure and removing dust or the like than reducing the pressure of the ink. But in the case of the unsatisfactory discharge caused by residual bubbles or the like, the bubbles may be dissolved into the ink by the pressurization and the bubbles may be again produced when the original pressure of the ink is restored. Thus the problem of unsatisfactory discharge cannot sometimes be substantially solved and therefore, it would be advantageous to use a method of reducing the pressure in a cap covering the fore end portion of the nozzle by a pump device and sucking ink from the fore end of the nozzle.
An example of the conventional pump device in such a case will hereinafter be described with reference to a schematic cross-sectional view shown in FIG. 1A of the accompanying drawings.
In FIG. 1A, reference numeral 1 designates a cylinder. By a piston 2 being moved down, negative pressure is produced in the space formed by the upper surface of the piston 2 and the cylinder 1. The air-tightness between the cylinder 1 and the piston 2 is kept by two O-rings 3 and 4. A valve denoted by 5 is lightly biased by a plate spring 6 so as to hermetically seal a hole 2-a provided in the piston. A cylinder stand 7 is hermetically sealed by an O-ring 8 so that the ink in the cylinder 1 may not flow outwardly. A compression spring 9 biases the piston 2 so as to return it to the upper point which is its initial position. Designated by 1-a is an ink inflow hole provided in the cylinder 1. A tube 112 for directing the ink sucked from the fore end of the nozzle of an ink jet head and a tube 105 for directing the sucked ink so as to keep the amount of ink in the head constant are connected to the ink inflow hole 1-a. Since it is inconvenient for moisture to evaporate through the walls of these tubes, the tubes cannot be formed of a soft material such as silicon rubber and therefore, the connected portions of these tubes must be hermetically sealed by bonding. Reference numeral 108 denotes a discharge tube for directing the air pressurized by the lower surface of the piston 2 and the cylinder 1 and the sucked ink to the outside of the cylinder. (This tube will pose a problem even if it is formed of silicon rubber and therefore, it is connected by forcing the outer sleeve of the discharge hole into the tube.)
Operation of the pump device will now be described.
When the piston 2 is depressed, the volume between the cylinder 1 and the piston 2 increases and therefore negative pressure is produced. At this time, the valve 5 is biassed into intimate contact with the hole 2-a of the piston by the plate spring 6 and the produced negative pressure and keeps air-tightness. When the piston is further depressed and the O-ring 4 passes through the inflow hole -a of the cylinder 1, ink and or air is sucked from the head by the negative pressure produced in the cylinder. Thereafter, the piston is further depressed and held at the lower point of the range of movement of the piston 2. Suction of ink and/or air is continuously effected in accordance with the negative pressure in the space formed at this time. When the suction of ink is terminated, the force which has depressed the piston 2 is eliminated and the piston is returned to the upper point by the spring 9. At this time, the sucked ink collects between the cylinder 1 and the upper surface of the piston 2 and little of the negative pressure remains. Therefore, when the piston 2 is moved up, positive pressure is produced between the cylinder 1 and the upper surface of the piston 2. The ink and air present between the cylinder 1 and the upper surface of the piston 2 flow out through the hole 2-a until the positive pressure overcomes the force of the plate spring 6 to open the valve 5 and the piston 2 returns to the upper point. The ink having thus flowed out collects in the space formed in the cylinder stand 7 and, when the piston 2 is then depressed, the ink is forcibly discharged out of the cylinder through the discharge hole 7-a.
However, in the pump of such a structure, when the O-ring 4 passes through the inflow hole 1-a, it snaps at a corner of the inflow hole 1-a as shown in the schematic illustration of FIG. 1B of the accompanying drawings and the O-ring is liable to be damaged. This is very undesirable when the durability or reliability of the O-ring is taken into consideration.
It is often the case that the latest ink jet recording apparatuses each have nozzles corresponding to four colors, i.e., yellow, magenta, cyan and black for color printing, and in such case, the number of tubes connected to the pump is great, e.g. eight, and the O-ring is more liable to be damaged. FIG. 1C of the accompanying drawings is a schematic cross-sectional view of the cylinder 1 at the level of the inflow hole 1-a. When molding a cylinder of such a structure, a mold for drawing out the cylinder horizontally is required in addition to a mold for drawing out the cylinder axially thereof and thus, the mold structure becomes complicated. Further, assuming that the number of nozzles is increased to increase the number of tubes connected to the pump to twice, i.e., sixteen, it is difficult to increase the number of inflow holes horizontally as viewed in FIG. 1c. If an inflow hole is provided at another level of the cylinder 1, the times during which ink is sucked from the respective inflow holes will differ from each other and therefore the amount of sucked ink will differ from inflow hole to inflow hole. This is inconvenient. If an attempt is made to increase the number of inflow holes at the same level, it will be accompanied by the necessity of adding inflow holes in the vertical direction as viewed in FIG. 1C, and this will lead to the necessity of using a mold for molding in this direction as well, which in turn will lead to complication of the mold structure.